The present invention relates to the field of soil mechanics, in particular to a system and method for electrochemical stabilization of soils of different types both on land and under water. The method and system of the invention may find use for protection of environment, stabilization of ocean, sea shores, and river banks from slides, as well as for strengthening of ocean and bay floors for extension of airport runways, for subgrade strengthening when constructing buildings and structures on weak or expansive soils, for construction of artificial shore structures in ocean and sea gulfs, bays, etc. The invention may also find use in oil recovery, mining, hydraulic engineering, irrigation, and road construction.
Soil or sand erosion by wind and water is a problem in most countries, especially for those with arid climates that are characterized by low rain fall, high solar radiation, high temperature and high evaporation rates.
The structure of soil determines its properties such as permeability to water, porosity, crust formation, load-carrying capacity, etc. Therefore, an improved soil structure will reduce soil erosion by wind or water. It will also reduce water evaporation, increase intra- and inter particle linkages and increase the bonding strength of agglomerates so that they can sustain heavy weights. It will also increase the infiltration rate and reduction of water run-off. Improved structures are needed because weak soil and sand structure are problematic in roads and highway slopes, embankments, water channels, construction excavation banks, landing sites such as civil and military air fields, sand dunes movement, military camps, oil fields and agriculture.
Furthermore, mankind has gravitated to the water-land interface or littoral areas along lakes, rivers, bays, sounds and oceans for residential, commercial and recreational purposes. To further these purposes, many fixed shoreline structures have been built at considerable effort and cost. However, Nature constantly, albeit generally slowly, changes these shorelines through erosion, storms, and even earthquakes.
Recent statistics and studies indicate that increasing amounts of damage are occurring yearly to salt water shoreline areas in particular due to higher tidal levels and storms of increasing severity. According to Eugene Linden, xe2x80x9cBurned by Warmingxe2x80x9d, TIME, Mar. 14, 1994 (pg. 79), xe2x80x9csuch problems can be expected to intensify in the near future.xe2x80x9d Among the erosion problems encountered are the gradual or rapid direct erosion of bluffs or slightly elevated shorelines, loss of sand and pebbles from beach surfaces, destruction of piers, boathouses and other protruding or exposed artificial structures, and the washing away of sand dunes along the shoreline. In many barrier island areas such as Long Island, N.Y. and in the Carolinas, barrier islands have been eroded to the extent that dune systems are destroyed, new inlets and channels are formed for the ocean and adjacent waterways, and buildings, roads and other manmade structures are destroyed and/or swept away.
Furthermore, according to Glen Martin, xe2x80x9cSan Francisco Chroniclexe2x80x9d, Mar. 20, 2000, the problems associated with landslides are encountered in California. For the last two years California experienced a number of catastrophic landslides.
For centuries efforts have been made to stabilize soils and reinforce shoreline areas to prevent destruction of soils and shorelines.
Known methods and systems for stabilization of soil can be roughly divided into mechanical, chemical, and electrochemical. Mechanical methods and systems involve creation of reinforcement structures or mixing of the soil with reinforcement materials such as fibers, etc. Normally, such methods and systems are extremely expensive and therefore are applicable only to relatively small areas of low thickness.
Pure chemical methods and systems are based on the use of chemical substances which are introduced into soil and chemically interact between each other in the soil to form new compounds which bind soil particles and thus stabilize the soil. However, the aforementioned chemical reagents are extremely expensive and therefore purely chemical methods and systems also have limited application.
Electrochemical methods, to which the present invention pertains, consist in introduction into the soil of relatively inexpensive chemical substarces with subsequent application of electrochemical energy which generates such processes as electrolysis, electroosmosis, change in pH value of the soil, etc. These processes, in turn, cause secondary chemical reactions which produce soil binding compounds and thus reinforce and stabilize soils.
For example, U.S. Pat. No. 5,616,235 issued to Acar, et al. on Apr. 1, 1997 discloses a method for electrochemical stabilization of soils and other porous media. This method strengthens a soil by the addition of a cementing agent comprising an anion and a cation, wherein the combination of the anion and cation in the soil forms a cementitious product. More specifically, the method consists of applying an electric field in the soil between an anode and a cathode, supplying water to the soil near the anode, introducing the cation to the soil near the anode, thus causing migration of cations through the soil in the direction from the anode towards the cathode, introducing the anion to the soil near the cathode, thus causing migration of anions through the soil in the direction from the cathode towards the anode; and either introducing a base to the soil near the anode to neutralize protons generated by electrolysis of water at the anode or introducing an acid to the soil near the cathode to neutralize hydroxide generated by electrolysis of water at the cathode, or both. As a result, the cations and the anions are dispersed through the soil between the anode and the cathode, and the combination of the anions and cations in the soil forms a cementitious product. The method also comprises the step of supplying water to the soil near the anode. The cations and the anions can be introduced in an alternating mode.
A disadvantage of the aforementioned methods consists in that the soil stabilization process involves a plurality of sequential operations for introduction of various chemicals into different areas where anodes and cathodes are located. In other words, the process requires zoning of the entire area to be treated and marking of separate zones. This is a complicated, expensive, and time- and labor-consuming process. Therefore such a method is difficult to realize in practice on a fairly large area. Furthermore, the process requires that positions of cathode and anodes be clearly marked for low-skilled workers to know where and when to inject an appropriate chemical.
Japanese Laid-Open Patent Application (Kokai) Hei 7-180,135 issued Jul. 18, 1995 to Hisao Inutsuka describes a method and a system for improving and strengthening poor subsoil and soil by arranging a cathode and an anode in proper positions in the subsoil and soil having a relatively small coefficient of water permeability. A flow of electric current is then generated between the anode and the cathode. The cathode and anode can be made in the form of bars or plates. The electrodes are inserted into the unsolidified and uncontracted soil, a flow of direct electric current is then generated between the electrodes with simultaneous supply of water into the treated area. As a result the area in the vicinity of the cathode is solidified and contracted. The polarity of the electrodes is then reversed, whereby the soil is solidified and contracted in the vicinity of the former anode, i.e., current cathode. The inventor further claims different power sources, such as solar energy, wind energy, tidal energy, thermal energy obtained from garbage incineration, etc. for use in the method. Prior to use, the obtained electric energy is rectified into a direct current.
A common disadvantage of all known processes and systems for stabilization of soil described above is that they result in a non-uniform distribution of strength in the stabilized soil. This is because the known processes and systems do not allow to control temperature in the soil during stabilization. However, the known methods described above are accompanied by rapid variation of pH in the near-electrode areas, and as a result, by rapid variations of temperatures which are different in various zones and layers of the soil. Moreover, reversing of polarity of the electrodes causes further variation in three phases of the soil, i.e., in salt composition of a liquid phase, in composition of a gaseous phase with intensive generation of hydrogen near the cathode and of oxygen near the anode, and as a result, in decomposition of a solid phase with the formation of carbon dioxide and other gases. The aforementioned phenomena, in turn, cause vigorous secondary reactions with intensive and non-uniform generation of heat in various layers and zones of the soil mass. This results in aforementioned non-uniform strength in various vertical and horizontal sections of the soil. Another consequence of the aforementioned phenomena is polarization of electrodes which leads to non-controlled drop of electric current in the circuits.
It is an object of the present invention to provide a system and a method for electrochemical stabilization of soil which are inexpensive, are applicable for treating large areas to a significant depth, have an expanded range of applications, do not require zoning and marking of separate areas, and ensure uniform distribution of strength in the stabilized soil. Another object is to provide a strengthened soil structure which does not form an obstacle for natural underground water flows.
Multiple rows of wells are drilled in the soil of the area to be stabilized, and then pairs of electrodes, i.e., an aluminum anode and a copper-graphite cathode connected to a source of a bipolar pulse electric current, are inserted into each well in such a manner that during operation all anodes of odd wells are connected to a positive terminal (for positive pulses) of the source, while all cathodes of even wells are connected to a negative terminal (for positive pulses) of the source. After a certain period of treatment the anodes and cathodes are reversed so that all anode of even wells are connected to the positive terminals of the source, whereas the cathodes of the odd wells are connected to the negative terminal of the source. Controlled directional structuring of the soil mass is carried out by adjusting the duration of current pulses, intervals between two sequential bipolar pulses of pulse current, and current density in the pulses. Prior to initiation of the soil stabilization process, salts which correspond to the type of treated soil are introduced into the wells. Furthermore, water under pressure is fed to the area of the soil being currently stabilized as an additional measure for controlling soil temperature.